Quantum-Classical Coexistence in Multi-Band Optical Networks: A Noise Analysis of QKD

In this letter, we propose to implement quantum key distribution (QKD) by using a multi-band strategy. We present a thorough noise analysis of quantum-classical coexistence while incorporating all relevant and precise noise parameters. Our research demonstrates that utilizing the entire extended C-band for quantum and transmitting classical channels (CChs) over the extended L-band with bandwidth of 75 GHz and power of 0 dBm yields no quantum communication beyond 13 km. To address the problem, we utilize the C+L-band to serve CChs and other bands (e.g., O, E, S) for quantum channels (QChs), while taking into account impairments over the quantum one. Results indicate that, while C+L-band is fully loaded, wavelengths of 1381 nm and below (1260-1381 nm) are appropriate for quantum signals, with 1381 nm offering the highest key rate (3.08 Mbit/sec) over a fiber length of 70 km. Finally, to explore an additional operational scenario when the network is not fully loaded, we focused on determining the optimal policy for assigning CChs. The results reveal the importance of prioritizing the maximization of the gap between the CChs and QChs. In addition, the channel assignment pattern of CChs affects the performance of QChs transmitted at other bands (O, E, and S).